In recent years, development of a lithium ion secondary battery has been actively advanced. Graphite is typically used for a negative electrode active material for the lithium ion secondary battery. However, further increase in capacity has recently been required for the lithium ion secondary battery with the increase of cruising distance of electric vehicles and multifunctionality of mobile terminals.
To this end, as a method to increase capacity of the lithium ion secondary battery, increase in capacity of a negative electrode active material, that is, a high capacity negative electrode of a metal series exemplified by Si series and Sn series has been examined. However, such a material exhibits large volume change accompanying charge and discharge, unfortunately causing crack of active material or drop off of the active material from a current corrector to deteriorate cycle characteristics.
PTL 1 has proposed SiO in which nanosized Si is dispersed in SiO2 to solve the above problems. This SiO indicates cycle characteristics better than those of Si.